1. Field of the Invention
The present invention relates to a driver circuit for driving a magnetic head that performs recording on a magnetic recording medium, and to a magnetic storage device which employs the driver circuit, and more particularly to a driver circuit for driving a write head which is provided spaced apart from a read head, and to a magnetic storage device.
2. Description of the Related Art
A magnetic recording system records data on a magnetic recording medium using a magnetic head, and magnetic disk devices and magnetic tape devices, and the like, are widely used. In such magnetic recording, an improvement in recording density and improvements in write speed and in read speed are being sought. In order to improve recording density, a magneto resistance element (or giant magneto resistance element), which is a highly sensitive magnetic sensor, is adopted.
On the other hand, since a magneto resistance element is read-only, in order to perform writing, it is necessary to separately provide a write element such as an inductive element. A driver circuit (write driver) is required to drive this write element. FIG. 10 is a constitutional view of a conventional write driver, and FIG. 11 is an explanatory view of the operation of the conventional write driver.
As shown in FIG. 10, the write driver circuit is constituted of an H bridge circuit comprising four NPN-type transistors 100, 102, 104, 106. In other words, pairs of NPN transistors 100 and 102, and 104 and 106, are serially connected in a vertical direction, and a write head (element) 120 is connected to nodes N, P of the pairs of NPN transistors.
Further, a positive potential is applied from a positive power source 110 to the collectors of the upper transistors 100, 104, and a negative power source 112 is connected to the emitters of the lower transistors 102, 106, such that drive is provided using two power sources. In other words, the upper transistors 100, 104 possess a function to supply a potential to the write element 120, and the lower transistors 102, 106 provide the function of causing a current to flow to the write element 120.
By way of explanation of the operation of the driver circuit, assuming that signals A, D of the transistors 100 and 106 are “high”, and that the signals B, C of the transistors 102 and 104 are “low”, the top left transistor 100 and the bottom right transistor 106 are ON, and, as shown by the dotted line in the figure, a write current flows from left to right in the write element (coil) 120.
On the other hand, also, as shown by the solid line, when a write current is flowing from right to left in the write element 120, signals A to D are inverted and the top right transistor 104 and the bottom left transistor 102 are ON. The value of this write current is controlled by a current source (for example, a resistor) 114 provided therebelow.
FIG. 11 is a transition diagram for the potentials of the nodes N, P on both ends of the write coil 120 when a write current is flowing. As shown in FIG. 11, assuming that the signals B, C of the transistors 104, 102 are “high” and the signals A, D of the transistors 100, 106 are “low”, the top right transistor 104 and the bottom left transistor 102 are ON, a write current flows from right to left in the write coil 120. At such time, since the write element 120 is a coil (inductance), after the voltages at both ends thereof have risen to a flyback voltage level, there is convergence between these voltages as a result of a counter electromotive force.
When a current flows from right to left in the write coil 120, the maximum values of this flyback voltage level are, at the node N, (+Vcc−the base potential of the transistor 104), and, at the node P, (−Vee+the base potential of the transistor 102).
With such an H bridge circuit, the application voltages applied to the upper transistors 100, 104, and the lower transistors 102, 106 are different. As a result, as shown in FIG. 11, the flyback voltage levels are vertically asymmetrical.
Meanwhile, in a magnetic storage device, as shown in FIG. 12, the magnetic head is constituted by integrating the write element 120 and a read element (MR element) 122, and the write element 120 and the read element 122 are connected via each of the nodes 132, 134, 136, 138 to an analog IC circuit 130 comprising the write driver described above and a read amp, or the like.
According to such a conventional write driver constitution, first, since the flyback voltage is vertically asymmetric, as shown in FIG. 11, the voltage in a center position of the write element 120 (known as the common voltage) also changes in accordance with a vertical flyback voltage difference. And a change to this transitional common voltage enters the read element 122, which is adjacent to the write element 120, as noise.
Also, with a two power-source system H bridge circuit, the common voltage of the write element 120 differs from the ground potential even if in a steady state since this common voltage is determined by the negative power source 112. Since this common voltage is not held at ground potential, the common potential enters the adjacent read element 122 as noise.
Meanwhile, in accordance with the demand in recent years for high density recording, a read element 122 suited to a narrow track width is being sought, for example, minimization of the read element core width to make same on the order of 0.3 to 0.4 micrometers is being sought. On account of such minimization of the core width, the withstand voltage of the read element becomes small.
Therefore, as a result of such noise, a state arises where voltages, which are equal to or greater than those required for the voltages at both ends of the read element, are applied, and there is a risk that, particularly with a read element of narrow core width, in the worst case, this will lead to the destruction of the read element. Even if not attributed to destruction of the read element, since the voltages at both ends of the read element change during writing, there is also the problem of the recovery time taken for the voltage of the read element to return to its original value at the time of write to read recovery.
Secondly, in order to implement high-speed writing, a high write frequency is required. As shown in FIG. 12, a write current flows via a connecting wire 132, the write element 120, and a connecting wire 134. Therefore, whenever the write speed increases, a transmission line impedance cannot be observed in the write waveform. However, in a conventional driver circuit, since no consideration is paid to the effects of reflection, as shown in FIG. 13, as a result of reflected waves, the write waveform rises slowly, and ringing is produced in the write waveform itself. High-speed writing is therefore problematic.